The overall goal of this project remains as stated in the original proposal: to examine the biological consequences of ultradian pulsatile secretion by the endocrine pancreas. We established that pulsatile delivery of glucagon to perfused rat hepatocytes was a more effective stimulus for glucose production than was continuous glucagon administration. We traced this "pulse- enhancement" effect to the temporal asymmetry of the hepatocyte response to glucagon, outlined the dependency of the effect on the frequency of pulse administration, and investigated the molecular mechanism leading to the critical asymmetry of the hepatocyte response. These results provide a strong empirical and theoretical foundation for the work to be performed in the coming two years. We propose to examine the consequences of pulsatile insulin secretion in the nonhuman primate. We will compare the effects of pulsatile and continuous portal insulin administration at the natural secretory interval of 10 minutes to determine the impact of ultradian secretion in normal physiology. Responses studied will include hepatic glucose production, glucose clearance, ketogenesis, lipolysis, glucose counterregulation, and entrainment of glucagon secretion. We will also examine the consequences of varying the interval at which insulin pulses are administered to primates in order to test our theory that insulin pulsatility is "tuned" to maximize the throughout of information to the liver. We will also assess the frequency-response characteristics of peripheral insulin-sensitive pathways to determine whether certain frequencies of pulsatile insulin replacement in diabetics might selectively enhance the hepatic effects of insulin.